Method and system for managing security in mobile communication system

ABSTRACT

A method, an apparatus, and a system for solving and managing security problems, which may occur during a handover of a User Equipment (UE) between PLMNs in a mobile communication network, by using a Non-Access Stratum (NAS) protocol are provided. By the method, a UE can perform a security mode command and an authentication with a network. Further, the method can prevent interruption of communication due to authentication or security during a handover of a UE between Public Land Mobile Networks (PLMNs).

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation application of prior application Ser.No. 14/844,737, filed on Sep. 3, 2015, which is a continuationapplication of prior application Ser. No. 14/532,421, filed on Nov. 4,2014, which issued as U.S. Pat. No. 9,131,380 on Sep. 8, 2015, andclaimed the benefit under 35 U.S.C §119(a) of a U.S. patent applicationfiled on Apr. 27, 2012, in the U.S. Patent and Trademark Office andassigned Ser. No. 13/504,786, which issued as U.S. Pat. No. 8,881,237 onNov. 4, 2014, and which was the U.S. National Stage application under 35U.S.C. §371 of an International Application filed on Oct. 27, 2010, andassigned application number PCT/KR2010/007430, which claimed the benefitunder 35 U.S.C. §365(b) of a Korean patent application filed in theKorean Industrial Property Office on Oct. 27, 2009, and assigned Serialnumber 10-2009-0102501, the entire disclosure of each of which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mobile communication system. Moreparticularly, the present invention relates to a method and a system formanaging a security and an authentication of a User Equipment (UE) and anetwork in an environment in which the UE performs a handover.

2. Description of the Related Art

The 3rd Generation Partnership Project (3GPP), which is a representativeorganization for establishing standards for a mobile communicationsystem, has defined an Evolved Packet System (EPS) for the nextgeneration communication and has employed the Mobility Management Entity(MME) as a mobility management entity of a network. For the mobilecommunication system as described above, a solution improved from theNon-Access Stratum (NAS) protocol, which has been used in theconventional mobile communication systems, such as a 3GPP communicationsystem, has been presented in order to provide a high speedcommunication service in the next generation mobile communication. Inthe improved solution, a security management scheme has been enhanced byemploying, in performing a security mode, the concept of a NAS protocol,which provides a security to a NAS, in addition to a security processperformed in a wireless access stratum and a conventional authenticationprocess.

However, according to the current NAS protocol definition and thecurrent NAS protocol security definition, the security may not beensured or the communication may be interrupted in supporting a handoverbetween Public Land Mobile Networks (PLMNs). Therefore, a need existsfor a method capable of supporting the communication, the security, andthe authentication between a UE and a network in an efficient andincessant manner even though the PLMN changes, through an improvement ofa NAS security mode command process introduced in order to enhance theNAS protocol and the authentication process.

The above information is presented as background information only toassist with an understanding of the present disclosure. No determinationhas been made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the present invention.

SUMMARY OF THE INVENTION

Aspects of the present invention are to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly, an aspect of the presentinvention is to provide a system and a method for security managementusing a Non-Access Stratum (NAS) protocol during a handover of a UE by amobility management entity in a mobile communication system.

Another aspect of the present invention is to provide a system and amethod for security management in a mobile communication system, whichenables smooth operations of authentication and security modes evenduring a handover of a User Equipment (UE) between Public Land MobileNetworks (PLMNs) by using a NAS protocol, thereby achieving an efficientmobility management of the UE.

In accordance with an aspect of the present invention, a method ofmanaging a security during a handover of a User Equipment (UE) by aMobility Management Entity (MME) of a mobile communication system isprovided. The method includes comparing a network identity included in aTracking Area Update (TAU) request message received from the UE with anetwork identity of the MME, and determining whether to transmit anauthentication request message, based on a result of the comparisonbetween the network identities.

In accordance with another aspect of the present invention, a method ofmanaging a security during a handover of a UE in a mobile communicationsystem is provided. The method includes transmitting a TAU requestmessage to an MME, and receiving an authentication request message fromthe MME according to a result of comparison between a network identityincluded in the TAU request message and a network identity of the MME.

In accordance with another aspect of the present invention, a method ofmanaging a security during a handover of a UE by an MME of a mobilecommunication system is provided. The method includes receiving a TAUrequest message from the UE, comparing a network identity included inthe TAU request message with a network identity of the MME, anddetermining whether to transmit a Security Mode Command (SMC) message tothe UE as a result of the comparison.

In accordance with another aspect of the present invention, a method ofmanaging a security during a handover of a UE in a mobile communicationsystem is provided. The method includes transmitting a TAU requestmessage to an MME, and receiving an SMC message from the MME accordingto a result of comparison between a network identity included in the TAUrequest message and a network identity of the MME.

In accordance with another aspect of the present invention, an apparatusfor managing a security during a handover of a UE by an MME of a mobilecommunication system is provided. The apparatus includes a control unitfor comparing a network identity included in a TAU request messagereceived from the UE with a network identity of the MME, and fordetermining whether to transmit an authentication request message, basedon a result of the comparison between the network identities.

In accordance with another aspect of the present invention, an apparatusfor managing a security during a handover of a UE in a mobilecommunication system is provided. The apparatus includes a control unitfor transmitting a TAU request message to an MME, and for receiving anauthentication request message from the MME according to a result ofcomparison between a network identity included in the TAU requestmessage and a network identity of the MME.

In accordance with another aspect of the present invention, an apparatusfor managing a security during a handover of a UE in a mobilecommunication system is provided. The apparatus includes a control unitfor transmitting a TAU request message to an MME, and for receiving anSMC message from the MME according to a result of comparison between anetwork identity included in the TAU request message and a networkidentity of the MME.

Other aspects, advantages, and salient features of the invention willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainexemplary embodiments of the present invention will be more apparentfrom the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a block diagram illustrating a Public Land Mobile Network(PLMN) handover and security environment in a mobile communicationsystem according to an exemplary embodiment of the present invention;

FIG. 2 is a message flow diagram illustrating a process ofauthentication during a handover between PLMNs according to an exemplaryembodiment of the present invention;

FIG. 3 is a message flow diagram illustrating a Security Mode Command(SMC) process during a handover between PLMNs according to an exemplaryembodiment of the present invention;

FIG. 4 is a message flow diagram illustrating an authentication processduring a handover between PLMNs according to an exemplary embodiment ofthe present invention;

FIG. 5 is a message flow diagram illustrating an authentication processduring a handover between PLMNs according to another exemplaryembodiment of the present invention;

FIG. 6 is a message flow diagram illustrating a Security Mode Command(SMC) process during a handover between PLMNs according to an exemplaryembodiment of the present invention;

FIG. 7 is a message flow diagram illustrating an SMC process during ahandover between PLMNs according to another exemplary embodiment of thepresent invention;

FIG. 8 is a flowchart illustrating an operation of a Mobile ManagementEntity (MME) for supporting an authentication process during a handoverbetween PLMNs according to an exemplary embodiment of the presentinvention;

FIG. 9 is a flowchart illustrating an operation of a UE for supportingan authentication process during a handover between PLMNs according toan exemplary embodiment of the present invention;

FIG. 10 is a flowchart illustrating an operation of an MME forsupporting an SMC process during a handover between PLMNs according toan exemplary embodiment of the present invention; and

FIG. 11 is a flowchart illustrating an operation of a User Equipment(UE) for supporting an SMC process during a handover between PLMNsaccording to an exemplary embodiment of the present invention.

Throughout the drawings, it should be noted that like reference numbersare used to depict the same or similar elements, features, andstructures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of exemplaryembodiments of the invention as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the embodiments described hereincan be made without departing from the scope and spirit of theinvention. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of theinvention. Accordingly, it should be apparent to those skilled in theart that the following description of exemplary embodiments of thepresent invention is provided for illustration purpose only and not forthe purpose of limiting the invention as defined by the appended claimsand their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

A main idea of the exemplary embodiments of the present invention is toprovide an incessant mobile communication for a mobile communicationsystem during a handover of a User Equipment (UE) between Public LandMobile Networks (PLMNs) by using a Non-Access Stratum (NAS) protocolwhich is a protocol between a UE and a Mobility Management Entity (MME).Further, exemplary embodiments of the present invention provide a methodof supporting an authentication and the security and management of a NASprotocol, which is a protocol between a UE and an MME forauthentication. The following detailed description of exemplaryembodiments of the present invention discusses a 3GPP-based EvolvedPacket System (EPS) system, Universal Terrestrial Radio Access Network(UTRAN), and GSM EDGE Radio Access Network (GERAN), although exemplaryembodiments of the present invention can be used by another mobilecommunication system using a NAS protocol.

Meanwhile, as shown in FIG. 1, the exemplary embodiment of the presentinvention shown in FIG. 1 proposes a method of supporting anauthentication and a security for communication between a UE and an MMEby using a NAS protocol when a UE moves from an Evolved UTRAN (EUTRAN)or another Radio Access Technology (RAT) to another EUTRAN, and thismethod can be applied to other mobile communication systems, which havesimilar technical backgrounds, channel types, network architectures, orprotocols, or perform similar operations with different protocols, withsmall modifications without departing from the scope of the presentinvention, as apparent to those skilled in the art.

FIG. 1 is a block diagram illustrating a PLMN handover and securityenvironment in a mobile communication system according to an exemplaryembodiment of the present invention. As an example, a 3GPP EPS systemstructure has been described in FIG. 1. The following description ofexemplary embodiments of the present invention mainly discussespotential problems associated with when a UE moves from a EUTRAN oranother RAT to another EUTRAN. According to exemplary embodiments of thepresent invention, the method can be used by another similar mobilecommunication system.

Referring to FIG. 1, an Evolved Node Base Station (E Node B; eNB)/RadioNetwork Controller (RNC) 133 establishes a radio access and performs acommunication with a UE 110 located within a service area of itself. TheUE 110 refers to a terminal or UE accessing a packet data network, suchas the Internet, through a Serving Gateway (SGW) 116. As describedherein, a Packet Data Network Gateway (PDN GW) 118 as an importantnetwork entity of a packet data network that serves as a Home Agent(HA).

Meanwhile, a Mobility Management Entity (MME)/Serving GPRS Support Node(SGSN) 135 performs a mobility management, a location management, and aregistration of a UE. Further, a Home Subscriber Server (HSS) 121 formanaging authentication information and service information for a userand a UE is connected to the MME/SGSN 135 through an interface.

A data path exists between the eNB/RNC 133 and the Serving GW 116, and acontrol path or an interface for managing the mobility of a UE existsbetween the MME/SGSN 135 and the Serving GW 116. According to exemplaryembodiments of the present invention, the UE 110 and the MME/SGSN 135communicate with each other using a NAS protocol stack, therebyperforming the mobility management and session management.

Exemplary embodiments of the present invention address a situation inwhich a UE 110 connected to a source network performs a handover. It isassumed that the source network may be one RAT among various types ofRATs, such as a EUTRAN, UTRAN, and GERAN, and the PLMN of the sourcenetwork is different from the PLMN to which the UE 110 will move. Thatis, exemplary embodiments of the present invention attempt to resolveproblems associated with a handover situation of a UE 110 in which thePLMN changes from PLMN A to PLMN B during the handoff of the UE 110 froma source network to a target network and the target network supports theEUTRAN. Therefore, when the UE 110 performs a handover from a sourcenetwork to a target network, the UE 110 is connected to the target eNB112, the target MME 114, and the target HSS 141, and receives a servicefrom them. FIGS. 2 to 11 will be described with reference to theabove-mentioned network according to exemplary embodiments of thepresent invention for an efficient operation and the UE 110 and the MME114 based on a NAS protocol.

FIG. 2 is a message flow diagram illustrating a process ofauthentication during a handover between PLMNs according to an exemplaryembodiment of the present invention.

Step 201 corresponds to a handover preparation step. That is, step 201corresponds to a step of requesting a core network to provide resources,which includes a step of making requests for resource preparation by thetarget eNB 112, the target MME 114, and the serving GW 116. In thisstep, a bearer context or mobility management context is transmittedfrom a source system to a target system for the requesting.

The handover preparation step includes the following sub-steps. When thesource eNB/RNC 133 transmits a “relocation required” message to thesource MME/SGSN 135 in step 201-1, the source MME/SGSN 135 forwards arelocation request message to the target MME 114 in step 201-3. Then, instep 201-5, the target MME 114 forwards a relocation response message tothe source MME/SGSN 135.

In step 211, the source MME/SGSN 135 sends a relocation command messageto the source eNB/RNC 133, thereby notifying the source eNB/RNC 133 thatthe handover preparation step has been completed. Then, the sourceeNB/RNC 133 transmits a handover command message to the UE 110 in step213, and the UE 110 issues a handover command to the target eNB 112 instep 215. When the UE 110 has performed a handover to the target eNB112, the target eNB 112 transmits a handover notification message to thetarget MME 114 in step 217. Thereafter, in step 219, if there is achange in the serving GW 116, a bearer modification request is made bythe target MME 114, the serving GW 116, or the PDN GW 118. In step 221,during the handover process, the UE 110 transmits a Tracking Area Update(TAU) request message to the target MME 114. Thereafter, the target MME114 inserts a PLMN Identity (ID) in a TAU response message, which is notshown in the drawings, and then sends the TAU response message to the UE110. Then, the UE 110 can obtain a network ID of the serving network,which provides a service to the UE 110. The network ID includes aserving network ID and the PLMN ID. Therefore, even though theauthentication thereafter is started in the target MME 114, no problemoccurs in the authentication because the UE 110 and the target MME 114share the PLMN ID (e.g., the ID of the PLMN B).

Referring to FIG. 2, when the target MME 114 transmits an authenticationrequest message to the UE 110 as in step 241 while the target MME 114processes the TAU request message received in step 221, the UE 110verifies an authentication vector in step 243. At this time, because theUE 110 has not received a response (e.g., TAU response message) inresponse to the TAU request message, the UE 110 uses the PLMN ID (e.g.,PLMN A), which is the currently known ID of the serving network, incalculation for verifying the authentication vector, which results in afailure in the verification of the entire authentication vector. As aresult, the Radio Resource Control (RRC) connection between the UE 110and the source eNB/RNC 133 is interrupted in step 245, which causes aproblem.

FIG. 3 is a message flow diagram illustrating a Security Mode Command(SMC) process during a handover between PLMNs according to an exemplaryembodiment of the present invention.

Referring to FIG. 3, the exemplary embodiment of the present inventionis described in relation to an example which is hereinafter referred toas SMC case 1.

Step 301 corresponds to a handover preparation step. Step 301 isidentical to the handover preparation step 201, so a detaileddescription thereof will be omitted here.

In step 311, the source MME/SGSN 135 sends a relocation command messageto the source eNB/RNC 133, thereby notifying the source eNB/RNC 133 thatthe handover preparation step has been completed. Then, the sourceeNB/RNC 133 transmits a handover command message to the UE 110 in step313, and the UE 110 issues a handover command to the target eNB 112.When the UE 110 completes the handover process to the target eNB 112 instep 315, the target eNB 112 transmits a handover notification messageto the target MME 114 in step 317. Thereafter, in step 319, if there isa change in the serving GW 116, etc., a bearer modification request ismade by the target MME 114, the serving GW 116, or the PDN GW 118. Instep 321, during the handover process, the UE 110 transmits a TrackingArea Update (TAU) request message to the target MME 114. Thereafter, thetarget MME 114 inserts a PLMN Identity (ID) in a TAU response message,which is not shown in the drawings, and then sends the TAU responsemessage to the UE 110. Then, the UE 110 can obtain a network ID of theserving network, which provides a service to the UE 110. Therefore, eventhough the security mode command process thereafter is started in thetarget MME 114, no problem occurs in executing the security mode commandsince the UE 110 and the target MME 114 share the PLMN ID (e.g., the IDof the PLMN B).

However, referring to FIG. 3, the target MME 114 transmits a securitymode command message to the UE 110 as in step 341 while it processes theTAU request message received in step 321. Then, in step 343, the UE 110searches for an authentication key through an NAS Key Set Identity(eKSI). At this time, because the UE 110 has not received a response(e.g., a TAU response message) in response to the TAU request message,the serving network ID currently known to the UE 110 is the PLMN ID(PLMN A). However, due to the same eKSI in spite of differentauthentication values KASME, a NAS encryption key, and a NAS integritykey are generated based on the different authentication keys.Thereafter, when the UE 110 verifies the NAS Message Authentication Code(MAC) value in step 345, the UE 110 fails in deciphering the MAC becausethe integrity keys are different. As a result, a Radio Resource Control(RRC) protocol connection between the UE 110 and the source eNB/RNC 133may be interrupted, which causes a problem. In step 351, the target MME114 transmits a TAU accept message to the UE 110. In the followingdescription of exemplary embodiments of the present invention (as shownin FIGS. 4 to 11), the operations of the UE are performed by a controlunit (not shown) within the UE, and the operations of the MME areperformed by a control unit (not shown) within the MME.

FIG. 4 is a message flow diagram illustrating an authentication processduring a handover between PLMNs according to an exemplary embodiment ofthe present invention.

Referring to FIG. 4, the exemplary embodiment of the present inventionis described in relation to the example identified as SMC case 1.

Step 401 corresponds to a handover preparation step. Step 401 isidentical to the handover preparation step 201, so a detaileddescription thereof will be omitted here.

In step 411, the source MME/SGSN 135 sends a relocation command messageto the source eNB/RNC 133, thereby notifying the source eNB/RNC 133 thatthe handover preparation step has been completed. Then, the sourceeNB/RNC 133 transmits a handover command message to the UE 110 in step413, and the UE 110 issues a handover command to the target eNB 112.When the UE 110 completes the handover process to the target eNB 112 instep 415, the target eNB 112 transmits a handover notification messageto the target MME 114 in step 417. Thereafter, in step 419, if there isa change in the serving GW 116, etc., a bearer modification request ismade by the target MME 114, the serving GW 116, the PDN GW 118, etc. Instep 421, during the handover process, the UE 110 transmits a TrackingArea Update (TAU) request message to the target MME 114. Thereafter, instep 423, the MME 114 compares the PLMN ID of the MME 114 itself and thePLMN ID included in the information transmitted from the UE 110. Whenthe two IDs are different, the MME 114 sends an identity request messageto the UE 110 in step 425. In step 427, the UE 110 transmits an identityresponse message including an International Mobile Station Identity(IMSI) of itself to the target MME 114. In step 429, the target MME 114transmits an authentication data request message to the HSS 141. In step431, the HSS 141 calculates an authentication vector based on a new PLMNidentity. Then, the HSS 141 transmits a random number (RAND), anauthentication key (KASME), and an authentication token (AUTN) to thetarget MME 114 through an authentication data response step as step 433.Thereafter, the target MME 114 transmits an authentication requestmessage including a serving network identity (i.e. PLMN identity) to theUE 110 in step 441. The authentication request message further includesan AUTN and a random challenge (RAND), which are a part of theauthentication vector, in addition to the PLMN identity. In step 443,the UE 110 verifies the authentication vector and calculates theauthentication key (K_(ASME)) by using the new PLMN identity transmittedfrom the MME 114. Thereafter, in step 445, the UE 110 transmits anauthentication response message to the target MME 114 in step 445. Atthis time, the authentication response message sent from the UE 110 tothe target MME 114 includes an RES, which is a response parametercalculated by the UE 110. The RES may include the calculatedauthentication key (K_(ASME)).

In the meantime, the target MME 114 verifies if a receivedauthentication response message is an authentication response messagetransmitted from the UE, to which the target MME itself has sent theauthentication request, by comparing the RES included in the receivedauthentication response message with an expected response (XRES).

Although FIG. 4 is based on an assumption that there is no transfer of aPLMN identity by the eNB/RNC 133 through a handover command in step 413,a PLMN identity may be transferred through a handover command by theeNB/RNC 133 in step 413 in the case of another embodiment(authentication case 3). Then, even when the TAU request message hasbeen transmitted from the UE 110 to the target MME 114 as in step 421,the UE 110 and the MME 114 can have the same PLMN ID even withoutperforming steps 423 to 441. Therefore, the authentication process,security process, and communication thereafter can be incessantlyperformed even though the target MME 114 transmits an authenticationrequest message in step 441.

FIG. 5 is a message flow diagram illustrating an authentication processduring a handover between PLMNs according to another exemplaryembodiment of the present invention.

Referring to FIG. 5, the exemplary embodiment of the present inventionis described in relation to an example which is hereafter referred to asSMC case 2.

Step 501 corresponds to a handover preparation step. Step 501 isidentical to the handover preparation step 201, so a detaileddescription thereof will be omitted here.

In step 511, the source MME/SGSN 135 sends a relocation command messageto the source eNB/RNC 133, thereby notifying the source eNB/RNC 133 thatthe handover preparation step has been completed. Then, the sourceeNB/RNC 133 transmits a handover command message to the UE 110 in step513, and the UE 110 issues a handover command to the target eNB 112.When the UE 110 completes the handover process to the target eNB 112 instep 515, the target eNB 112 transmits a handover notification messageto the target MME 114 in step 517. Thereafter, in step 519, if there isa change in the serving GW 116, etc., a bearer modification request ismade by the target MME 114, the serving GW 116, the PDN GW 118, etc. Instep 521, during the handover process, the UE 110 transmits a TrackingArea Update (TAU) request message to the target MME 114. Thereafter, instep 523, the target MME 114 compares the PLMN ID of the MME 114 itselfwith the PLMN ID included in the information transmitted from the UE110. Then, in step 541, when the two IDs are different, which impliesthat the serving network identities (PLMN identities) are different, theMME 114 does not send an authentication request message to the UE 110until the processing of the TAU request message in step 521 iscompleted.

FIG. 6 is a message flow diagram illustrating a Security Mode Command(SMC) process during a handover between PLMNs according to an exemplaryembodiment of the present invention.

Referring to FIG. 6, the exemplary embodiment of the present inventionis described in relation to the example identified as SMC case 1.

Step 601 corresponds to a handover preparation step. Step 601 isidentical to the handover preparation step 201, so a detaileddescription thereof will be omitted here.

In step 611, the source MME/SGSN 135 sends a relocation command messageto the source eNB/RNC 133, thereby notifying the source eNB/RNC 133 thatthe handover preparation step has been completed. Then, the sourceeNB/RNC 133 transmits a handover command message to the UE 110 in step613, and the UE 110 issues a handover command to the target eNB 112.When the UE 110 completes the handover process to the target eNB 112 instep 615, the target eNB 112 transmits a handover notification messageto the target MME 116 in step 617. Thereafter, in step 619, if there isa change in the serving GW 116, etc., a bearer modification request ismade by the target MME 116, the serving GW 116, the PDN GW 118, etc. Instep 621, during the handover process, the UE 110 transmits a TrackingArea Update (TAU) request message to the target MME 116. Thereafter, instep 623, the target MME 116 compares the PLMN ID of the MME 116 itselfwith the PLMN ID included in the information transmitted from the UE110. When the two IDs are different and the target MME 114 has acquiredan authentication key (K_(ASME)) for a new PLMN identity, the target MME114 generates a NAS integrity key (K_(NAS)int) and a NAS encryption key(K_(NAS)enc) in step 625. Thereafter, in step 641, the target MME 114inserts a serving network identity (i.e., a PLMN identity) in a SecurityMode Command (SMC) message and transmits the SMC message to the UE 110.In step 643, the UE 110 acquires an authentication key through a NAS KeySet Identity (eKSI). At this time, the UE 110 acquires theauthentication key through an eKSI corresponding to the correspondingPLMN identity by using the newly received PLMN identity information, andgenerates a NAS integrity key (K_(NAS)int) and a NAS encryption key(K_(NAS)enc) from the authentication key. Thereafter, in step 645, theUE 110 verifies a NAS Message Authentication Code (MAC) by using the NASintegrity key (K_(NAS)int). When the verification is a success, the UE110 transmits a NAS security mode completion message in step 647.

Although FIG. 6 is based on an assumption that there is no transfer of aPLMN identity by the eNB/RNC 133 through a handover command in step 613,a PLMN identity may be transferred through a handover command by theeNB/RNC 133 in step 613 in the case of another exemplary embodiment ofthe present invention described in relation to an example which ishereinafter referred to as SMC case 3. Then, even when the TAU requestmessage has been transmitted from the UE 110 to the target MME 114 as instep 621, the UE 110 and the MME 114 can have the same PLMN ID evenwithout performing steps 623 to 641. Therefore, the authenticationprocess, security process, and communication thereafter can beincessantly performed even though the target MME 114 transmits an SMCmessage in step 641.

FIG. 7 is a message flow diagram illustrating an SMC process during ahandover between PLMNs according to another exemplary embodiment of thepresent invention.

Referring to FIG. 7, the exemplary embodiment of the present inventionis described in relation to the example identified as SMC case 2.

Step 701 corresponds to a handover preparation step. Step 701 isidentical to the handover preparation step 201, so a detaileddescription thereof will be omitted here.

In step 711, the source MME/SGSN 135 sends a relocation command messageto the source eNB/RNC 133, thereby notifying the source eNB/RNC 133 thatthe handover preparation step has been completed. Then, the sourceeNB/RNC 133 transmits a handover command message to the UE 110 in step713, and the UE 110 issues a handover command to the target eNB 112.When the UE 110 completes the handover process to the target eNB 112 instep 715, the target eNB 112 transmits a handover notification messageto the target MME 114 in step 717. Thereafter, in step 719, if there isa change in the serving GW 116, etc., a bearer modification request ismade by the target MME 114, the serving GW 116, the PDN GW 118, etc. Instep 721, during the handover process, the UE 110 transmits a TrackingArea Update (TAU) request message to the target MME 114. Thereafter, instep 723, the target MME 114 compares the PLMN ID of the MME 114 itselfwith the PLMN ID included in the information transmitted from the UE110. Then, in step 741, when the two PLMN identities are different andthe target MME 114 has acquired an authentication key (K_(ASME)) for anew PLMN identity through an authentication process, the target MME 114does not send an SMC message based on the new authentication key to theUE 110 until the processing of the TAU request message is completed.

FIG. 8 is a flowchart illustrating an operation of an MME for supportingan authentication process during a handover between PLMNs according toan exemplary embodiment of the present invention.

Referring to FIG. 8, in step 801, the target MME 114 performs a handoverpreparation process. Step 801 is identical to the handover preparationstep 201, so a detailed description thereof will be omitted here. Instep 803, the target MME 114 performs a process before receiving a TAUrequest message among the handover process. In step 805, the target MME114 determines the serving network identity (i.e., PLMN identity)through various comparisons, for example, by comparing the PLMN ID ofthe target MME 114 with a PLMN ID within an old GUTI of the TAU messagetransmitted from the UE 110 or by comparing the PLMN ID of the targetMME 114 with a PLMN ID of a last-visited TAI within the TAU messagetransmitted from the UE 110. When the PLMN IDs are different, onesolution is that the target MME 114 does not send an authenticationrequest message to the UE 110 until the processing of the TAU message iscompleted as in step 811. Another solution (e.g., case 1) is that thetarget MME 114 sends an identity request message to the UE 110 andreceives an identity response message from the UE 110 as in step 821.Thereafter, as in step 823, the target MME 114 transmits anauthentication data request message to the HSS 141 by using UE identityinformation and receives a new authentication vector as a response. Instep 825, the target MME 114 sends an authentication request messagetogether with a serving network ID (i.e. PLMN ID) to the UE 110. Then,in step 841, the target MME 114 receives an authentication responsemessage and verifies the response value.

FIG. 9 is a flowchart illustrating an operation of a UE for supportingan authentication process during a handover between PLMNs according toan exemplary embodiment of the present invention.

Referring to FIG. 9, in step 901, the UE 110 performs a handoverpreparation process. Step 901 is identical to the handover preparationstep 201, so a detailed description thereof will be omitted here. Instep 903, the UE 110 performs a process before sending a TAU requestmessage among the handover process. In step 921, the UE 110 receives anidentity request message from the target MME 114 and sends an identityresponse message to the target MME 114 as a response to the identityrequest message in step 921. In step 925, the UE 110 receives anauthentication request message including a serving network ID (i.e.,PLMN ID) from the target MME 114. Then, in step 931, the UE 110 verifiesan authentication token, calculates a response value (RES), andcalculates an authentication key (K_(ASME)) by using the serving networkID. Thereafter, in step 941, the UE 110 transmits an authenticationresponse message to the target MME 114.

FIG. 10 is a flowchart illustrating an operation of an MME forsupporting an SMC process during a handover between PLMNs according toan exemplary embodiment of the present invention.

Referring to FIG. 10, in step 1001, the target MME 114 performs ahandover preparation process. Step 1001 is identical to the handoverpreparation step 201, so a detailed description thereof will be omittedhere. In step 1003, the target MME 114 performs a process beforereceiving a TAU request message among the entire handover process. Instep 1005, the target MME 114 determines the serving network identity(i.e., PLMN identity) through various comparisons, for example, bycomparing the PLMN ID of the target MME 114 with a PLMN ID within an oldGUTI of the TAU message transmitted from the UE 110 or by comparing thePLMN ID of the target MME 114 with a PLMN ID of a last-visited TAIwithin the TAU message transmitted from the UE 110. When the PLMN IDsare different, one solution is that the target MME 114 does not send anSMC message to the UE 110 until the processing of the TAU message iscompleted as in step 1011. Another solution (e.g., case 1) is that, whenthe MME 114 has acquired a new authentication key (K_(ASME)) through anew authentication, the target MME 114 generates a NAS encryption keyand a NAS integrity key as in step 1021. Then, in step 1025, the targetMME 114 sends a NAS SMC message together with a serving network ID(i.e., PLMN ID) to the UE 110. Then, in step 1041, the target MME 114receives a security mode completion message from the UE 110.

FIG. 11 is a flowchart illustrating an operation of a UE for supportingan SMC process during a handover between PLMNs according to an exemplaryembodiment of the present invention.

Referring to FIG. 11, in step 1101, the UE 110 performs a handoverpreparation process. Step 1101 is identical to the handover preparationstep 201, so a detailed description thereof will be omitted here. Instep 1103, the UE 110 performs a process before sending a TAU requestmessage among the entire handover process. In step 1125, the UE 110receives an SMC message including a serving network ID (i.e., PLMN ID)from the target MME 114. Then, in step 1131, the UE 110 generates a NASencryption key and a NAS integrity key based on an authentication keyindexed by an eKSI, wherein the UE 110 finds an eKSI corresponding tothe newly received PLMN ID. In step 1133, the UE 110 verifies a MessageAuthentication Code (MAC) by using the NAS integrity key. Thereafter, instep 1141, the UE 110 transmits a security mode completion message tothe target MME 114.

According to exemplary embodiments of the present invention, asdescribed above with reference to FIGS. 4 to 11, it may be necessary tosupport messages shown in Tables 1 to 3 for operations of the UE and theMME, which will be described hereinafter.

Table 1 below shows types of authentication request messages accordingto exemplary embodiments of the present invention. Although the messagetypes shown in Table 1 are used when the messages are transmitted fromthe target MME 114 to the UE 110 as in step 441 of FIG. 4, exemplaryembodiments of the present invention are not limited to the shownmessage types. Detailed information on the PLMN IDs of Table 1 can bereferred to Table 3.

TABLE 1 Pres- For- IEI Information element Type/Reference ence matLength Protocol discriminator Protocol M V ½ discriminator 9.2 Securityheader type Security header type M V ½ 9.3.1 Authentication requestMessage type M V  1 message type 9.8 NAS key set NAS key set M V ½identifier_(ASME) identifier 9.9.3.21 Spare half octet Spare half octetM V ½ 9.9.2.9 Authentication Authentication M V 16 parameter RANDparameter RAND (EPS challenge) 9.9.3.3 Authentication Authentication MLV 17 parameter AUTN (EPS parameter AUTN challenge) 9.9.3.2 PLMNIdentity PLMN identity O V  3 x.x.x.x (spec section number)

Table 2 below shows types of SMC messages according to exemplaryembodiments of the present invention. Although the message types shownin Table 2 are used when the messages are transmitted from the targetMME 114 to the UE 110 as in step 641 of FIG. 6, exemplary embodiments ofthe present invention are not limited to the shown message types.Detailed information on the PLMN IDs of Table 2 can be referred to Table3.

TABLE 2 IEI Information Element Type/Reference Presence Format LengthProtocol discriminator Protocol discriminator M V ½ 9.2 Security headertype Security header type M V ½ 9.3.1 Security mode command Message typeM V 1 message identity 9.8 Selected NAS security NAS security M V 1algorithms algorithms 9.9.3.23 NAS key set identifier NAS key setidentifier M V ½ 9.9.3.21 Spare half octet Spare half octet M V ½9.9.2.9 Replayed UE security UE security capability M LV 3-6capabilities 9.9.3.36 C- IMEISV request IMEISV request O TV 1 9.9.3.1855 Replayed nonce_(UE) Nonce O TV 5 9.9.3.25 56 Nonce_(MME) Nonce O TV 59.9.3.25 PLMN Identity PLMN identity O V 3 x.x.x.x

Table 3 below shows PLMN ID Information Elements (IEs) included in theauthentication request message or the SMC message of Tables 1 and 2according to exemplary embodiments of the present invention, whichcorrespond to IEs for notifying of information to be included in orderto send the PLMN identities to the UE 110. Further, the PLMN ID IEs arenot limited to the message types shown in Table 3. The PLMN ID IEs areIEs of type 3 and have a length of 4 octets. The MCC indicates a MobileCountry Code, in which octet 2 and octet 3 are configured in bits 1 to4, and the MNC indicates a Mobile Network Code, in which octet 4 andoctet 3 are configured in bits 5 to 8.

TABLE 3 8 7 6 5 4 3 2 1 PLMN identity IEI octet 1 MCC digit 2 MCC digit1 octet 2 MNC digit 3 MCC digit 3 octet 3 MNC digit 2 MNC digit 1 octet4 MCC, Mobile country code (octet 3, octet 4 bits 1 to 4) The MCC fieldis coded as in ITU-T Rec. E212, Annex A. MNC, Mobile network code (octet5, octet 4 bits 5 to 8). The coding of this field is the responsibilityof each administration but BCD coding shall be used. The MNC shallconsist of 2 or 3 digits. For PCS 1900 for NA, Federal regulationmandates that a 3-digit MNC shall be used. However a network operatormay decide to use only two digits in the MNC over the radio interface.In this case, bits 5 to 8 of octet 4 shall be coded as “1111”. Mobileequipment shall accept MNC coded in such a way.

In a mobile communication network according to exemplary embodiments ofthe present invention, when a UE performs a handover between PLMNs,especially when a UE performs a handover from a EUTRAN or another RAT(e.g., such as GETRAN or UTRAN) to another EUTRAN, it is possible toresolve problems associated with the authentication and security of theUE, thereby preventing interruption of communication.

Further, exemplary embodiments of the present invention propose a methodcapable of smoothly performing an authentication of a UE and a securitymode command for the UE even during a handover of the UE between PLMNsby using a NAS protocol, so as to achieve an efficient mobilitymanagement of the UE.

While the invention has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method for performing a security procedure by aterminal in a mobile communication system, the method comprising:transmitting, to a mobility management entity (MME), a tracking areaupdate (TAU) request message including a public land mobile networkidentity (PLMN ID) after a handover of the terminal; receiving, from theMME, a TAU response message in response to the TAU request message;receiving, from the MME, an authentication request message if the PLMNID included in the TAU request message is different from a PLMN ID of acell and a TAU procedure is complete, and transmitting, to the MME, anauthentication response message including an authentication responseparameter if an authentication is accepted.
 2. The method of claim 1,wherein the terminal is camped on the cell.
 3. The method of claim 1,further comprising: receiving a security mode command (SMC) message fromthe MME if the PLMN ID included in the TAU request message is differentfrom the PLMN ID of the cell and the TAU procedure is complete.
 4. Themethod of claim 1, wherein the PLMN ID of the cell is one of a pluralityof PLMN IDs managed by the MME.
 5. The method of claim 1, wherein, ifthe PLMN ID included in the TAU request message is different from thePLMN ID of the cell, the method further comprises: transmitting anidentity response message including an identity of the terminal to theMME as a response to a request for the identity of the terminal from theterminal; receiving an authentication request message including a firstauthentication key, an authentication vector, and the PLMN ID of thecell from the MME; generating a second authentication key based on thePLMN ID of the cell if the authentication is accepted; and transmittingan authentication response message including the second authenticationkey to the MME as a response to the authentication request message.
 6. Aterminal apparatus for performing a security procedure by a terminal ina mobile communication system, the apparatus comprising: a transceiverconfigured to transmit and receive messages; and a controller configuredto: transmit, to a mobility management entity (MME), a tracking areaupdate (TAU) request message including a public land mobile networkidentity (PLMN ID) after a handover of the terminal, receive, from theMME, a TAU response message in response to the TAU request message,receive, from the MME, an authentication request message if the PLMN IDincluded in the TAU request message is different from a PLMN ID of acell and a TAU procedure is complete, and transmit, to the MME, anauthentication response message including an authentication responseparameter if an authentication is accepted.
 7. The apparatus of claim 6,wherein the terminal is camped on the cell.
 8. The apparatus of claim 6,wherein the controller is further configured to receive a security modecommand (SMC) message from the MME if the PLMN ID included in the TAUrequest message is different from the PLMN ID of the cell and the TAUprocedure is complete.
 9. The apparatus of claim 6, wherein the PLMN IDof the cell is one of a plurality of PLMN IDs managed by the MME. 10.The apparatus of claim 6, wherein, if the PLMN ID included in the TAUrequest message is different from the PLMN ID of the cell, thecontroller is further configured to: transmit an identity responsemessage including an identity of the terminal to the MME as a responseto a request for the identity of the terminal from the terminal, receivean authentication request message including a first authentication key,an authentication vector, and the PLMN ID of the cell from the MME,generate a second authentication key based on the PLMN ID of the cell ifthe authentication is accepted, and transmit an authentication responsemessage including the second authentication key to the MME as a responseto the authentication request message.